Description of the Related Art
The invention relates to a device and method for detecting the coil temperature especially of a direct-current motor, and especially a brushless d-c motor, by determining the ohmic resistance or resistivity of at least one coil of the motor.
It is generally known that when a direct-current motor is running, it is particularly the coil thereof that is heated, and therefore during full-load running or operation or under extreme conditions of use, the heating of the coil requires special attention. For this purpose, different temperature-measuring devices have become known heretofore.
A first possibility for determining the coil temperature is known, for example, wherein a temperature sensor is provided in the coil by means of which the temperature of the coil can be measured. However, this device has the disadvantage that the temperature can only be measured at the very location of the sensor. This means that excessive local temperature rises in other regions of the coil or the mean temperature or total temperature distribution in the coil cannot be measured.
Another possibility for measuring the coil temperature is known wherein the ohmic resistance or resistivity of the coil is measured and the temperature increase is determined from this measured resistance value and a reference value i.e. a resistance value of the coil when the motor is cold. This procedure can only be employed, however, when the motor is at a standstill, and is therefore unsuitable for monitoring the motor temperature while the motor is running.
It is accordingly an object of the invention to provide a device and method for detecting or determining the coil temperature in a motor, by which the temperature of the entire coil at arbitrary running conditions of the motor is determined.